Short answer. Gevurah ("strength," also called Din, "judgment") is the fifth sefirah on the Kabbalistic Tree of Life: the divine power of limit, boundary, and judgment, anchoring the left pillar. Its counterpart is Chesed, overflowing lovingkindness; their balance is Tiferet, beauty. The tradition's own warning is the heart of it: severity uncoupled from mercy is, in the Zohar's picture, the very root of evil.
A power that says no
In the Kabbalistic map of the divine life, God unfolds through ten sefirot: ten emanations, usually drawn as a tree with three pillars. Gevurah, "strength," is the fifth. The classical sources also call it Din, "judgment," and the left column it anchors is the side of severity, named for it. It is the power that draws boundaries, that weighs, withholds, restrains, says no. Directly opposite stands Chesed, lovingkindness: boundless, pouring, the power that gives without first asking what the receiver deserves. The tradition mapped its founding figures onto the pair: Abraham, who fed strangers, is Chesed; Isaac, bound on the altar (Genesis 22), is Gevurah.
The point of the architecture is that neither side is meant to rule. Their reconciliation is Tiferet, "beauty," the harmonizing heart of the Tree. Mercy alone would drown creation in undifferentiated giving; judgment alone would burn it down. And limit is not the embarrassing sefirah. Nothing exists as itself without a boundary that says where it ends; in the later Lurianic school, as Scholem describes it, the first act of creation is itself a contraction, God withdrawing to make room for a world. In this picture, the no comes before the yes.
(One caveat owed up front: Kabbalah is a living Jewish tradition with its own teachers and its own interior life. This page borrows the lens as the scholarship presents it (Scholem, Tishby) and does not claim to speak for the tradition.)
The tradition's own warning
Here is the part the dictionaries skip, and it is the drama of the whole system. On the mainstream scholarly reading of the Zohar (Scholem in Major Trends in Jewish Mysticism (1941) and Kabbalah (1974), Tishby in The Wisdom of the Zohar (1989)), evil is not an alien power invading from outside. The demonic realm, the sitra achra ("the other side"), is born when severity breaks loose from mercy: Gevurah uncoupled, judgment that no longer answers to lovingkindness, a fire that has left the hearth and begun to feed on itself. Evil, in the Zoharic picture, is not the opposite of the divine attributes but one of them: isolated, hypertrophied, self-consuming.
Read that twice, because it cuts both ways. The system never says severity is evil; severity inside the balance is what makes justice, discipline, and a world with edges possible at all. It says severity alone is evil, and that the failure mode of strength is not weakness but unaccountability.
About "the angel of Gevurah"
One precision the internet rarely offers. You will read that Khamael (or Camael) is "the angel of Gevurah" and that the name means "the severity of God." Handle that carefully: the association comes from the later esoteric tradition (early-modern and occult Kabbalah, systematized in the Golden Dawn era), and the etymology is a gloss, not a finding. It is a traditional correspondence, and you may use it as one; it is not classical angelology, and the Zohar's own picture of Gevurah does not depend on it. The biblical name Kemuel, for what it is worth, means something more like "raised of God" or "assembly of God." Enjoy the correspondences; just know which century they come from.
What it means when you put the book down
This last move is the flagship's own construction, an ethic built with the Kabbalistic lens, held as a wager rather than offered as a finding. Mercy that meets no resistance is not kindness; it is permission. Severity that answers to no standard is not justice; it is cruelty with a vocabulary. Each failure looks like the virtue it betrays, which is why both are so popular. Gevurah is only safe when it obeys: when the standard binds the wielder before it binds anyone else, when the fire cuts the hand that holds it before it ever touches another person. Strength that exempts itself has already crossed, by the tradition's own definition, to the other side.
Common questions
What does Gevurah mean?
Gevurah means "strength," and the classical sources also call it Din, "judgment." It is the fifth sefirah on the Kabbalistic Tree of Life: the divine power of limit, boundary, and judgment, the power that weighs, withholds, restrains, and says no. It anchors the left column, the side of severity, named for it.
What is the difference between Gevurah and Chesed?
They are opposites held in balance. Gevurah is the power that draws boundaries and says no, while Chesed is lovingkindness: boundless, pouring, the power that gives without first asking what the receiver deserves. The tradition maps its founding figures onto the pair, Abraham (who fed strangers) as Chesed and Isaac (bound on the altar, Genesis 22) as Gevurah, and their reconciliation is Tiferet, "beauty," the harmonizing heart of the Tree.
Is Gevurah evil?
No, and the system is careful here. Severity inside the balance is what makes justice, discipline, and a world with edges possible at all; the sitra achra ("the other side") is born only when severity breaks loose from mercy, Gevurah uncoupled, a fire that has left the hearth and begun to feed on itself. On the mainstream scholarly reading of the Zohar (Scholem, Tishby), evil is severity alone, isolated and self-consuming, not severity as such.
Is Khamael the angel of Gevurah?
You will read that Khamael (or Camael) is "the angel of Gevurah" and that the name means "the severity of God," but handle that carefully. The association comes from the later esoteric tradition, early-modern and occult Kabbalah systematized in the Golden Dawn era, and the etymology is a gloss, not a finding. It is a traditional correspondence you may use as one; it is not classical angelology, and the Zohar's own picture of Gevurah does not depend on it.
This is the short version of the idea the flagship's final book is built on: the fire, held inside the standard it answers to.
Sources
G. Scholem, Major Trends in Jewish Mysticism (1941); G. Scholem, Kabbalah (1974); I. Tishby, The Wisdom of the Zohar (1989); Genesis 22.